Large Language Models (LLMs) are advanced AI systems trained on massive text datasets to understand and generate human-like text. These transformer-based models can perform diverse tasks including writing, coding, analysis, and conversation. LLMs power chatbots, assist in programming, enable content creation, and drive AI applications across industries. Popular models include OpenAI's GPT series, Anthropic's Claude, Google's Gemini, and Meta's LLaMA. They vary in capabilities, context windows, and pricing, with some available as free tiers and others requiring subscriptions for advanced features.